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Abstract:

A liquid discharge head includes a recording element substrate including
an energy generation element for generating energy used to discharge a
liquid and a terminal electrically connected to the energy generation
element, and an electric wiring board including an electrode electrically
connected to the terminal via a wire to transmit an electric signal
supplied from outside to the energy generation element, wherein the
terminal has an area twice or more larger than a contact area between the
terminal and the wire and the electrode has an area twice or more larger
than a contact area between the electrode and the wire.

Claims:

1. A liquid discharge head, comprising: a recording element substrate
including an energy generation element for generating energy used to
discharge a liquid and a terminal electrically connected to the energy
generation element; and an electric wiring board including an electrode
electrically connected to the terminal via a wire to transmit an electric
signal supplied from outside to the energy generation element, wherein
the terminal has an area twice or more larger than a contact area between
the terminal and the wire and the electrode has an area twice or more
larger than a contact area between the electrode and the wire.

2. The liquid discharge head according to claim 1, further comprising a
wire connecting a first region on a side of the electric wiring board
from a center of the terminal in a longitudinal direction of the terminal
and a second region on a side opposite to a side of the recording element
substrate from a center of the electrode in a longitudinal direction of
the electrode.

3. The liquid discharge head according to claim 1, further comprising: a
first wire connecting a first region on a side of the electric wiring
board from a center of the terminal in a longitudinal direction of the
terminal and a second region on a side opposite to a side of the
recording element substrate from a center of the electrode in a
longitudinal direction of the electrode; and a second wire connecting a
third region on a side opposite to the side of the electric wiring board
from the center of the terminal in the longitudinal direction of the
terminal and a fourth region on the side of the recording element
substrate from the center of the electrode in the longitudinal direction
of the electrode.

4. The liquid discharge head according to claim 3, wherein the number of
bending portions of the first wire is larger than the number of bending
portions of the second wire.

5. The liquid discharge head according to claim 3, wherein an interval
between the first region and the second region is equal to an interval
between the third region and the fourth region.

6. The liquid discharge head according to claim 1, further comprising a
support substrate configured to support the recording element substrate
and the electric wiring board, wherein an interval between the terminal
and the support substrate is larger than an interval between the
electrode and the support substrate.

7. A method for manufacturing a liquid discharge head, comprising: a step
for preparing a recording element substrate including an energy
generation element for generating energy used to discharge a liquid and a
terminal electrically connected to the energy generation element and an
electric wiring board including an electric wiring and an electrode
connected to the electric wiring; a first connection step for connecting
a first region of the terminal and a second region of the electrode by a
first wire; an inspection step for checking electric conduction of
portions connected by the first wire; a removal step for removing the
first wire determined to be defective in the inspection step; and a
second connection step for connecting a third region that is different
from the first region in the terminal from which the wire has been
removed and a fourth region that is different from the second region in
the terminal from which the wire has been removed.

8. The method for manufacturing the liquid discharge head according to
claim 7, wherein the first region is a region on a side of the electric
wiring board from a center of the terminal in a longitudinal direction of
the terminal, the second region is a region on a side opposite to a side
of the recording element substrate from a center of the electrode in a
longitudinal direction of the electrode, the third region is a region on
a side opposite to the side of the electric wiring board from the center
of the terminal in the longitudinal direction of the terminal, and the
fourth region is a region on the side of the recording element substrate
from the center of the electrode in the longitudinal direction of the
electrode.

9. The method for manufacturing the liquid discharge head according to
claim 7, wherein a plurality of bending portions is formed in the first
wire in the first connection step and bending portions whose number is
smaller than the number of bending points of the first wire are formed in
the second wire in the second connection step.

Description:

BACKGROUND OF THE INVENTION

[0001] 1Field of the Invention

[0002] The present invention relates to a liquid discharge head that
performs a recording operation by discharging a liquid such as ink to a
recorded medium such as recording paper and a method for manufacturing
the liquid discharge head.

[0003] 2. Description of the Related Art

[0004] In a conventional liquid discharge head, bump bonding or wire
bonding to a tape automated bonding (TAB) film is used in an electric
connection technique between a recording element substrate and an
electric wiring board such as a flexible wiring board. Further, a
full-line type liquid discharge head including a liquid discharge head
having a width comparable to a print width is known as a form of the
liquid discharge head.

[0005] The flexible wiring board applied to a full-line type liquid
discharge head is used to apply an electric signal for discharging ink to
the recording element substrate from outside. The flexible wiring board
includes an electrode terminal corresponding to an electrode of the
recording element substrate and an external signal input terminal
positioned at a wiring edge to receive an electric signal from a
recording apparatus body. The flexible wiring board and the recording
element substrate are electrically connected by a wire bonding technique
using a gold wire or the like. The electrode of the recording element
substrate, the electrode terminal of the flexible wiring board, and the
gold wire are sealed by a sealing agent and protected from corrosion by
ink or an external impact.

[0006] Ball bonding is commonly used as the wire bonding technique. The
shape of a wire after wire bonding is generally a mountain shape in which
the wire rises up from a wire start-edge and passes a bending point
before reaching a wire end-edge. In recent years, however, various
low-loop formation techniques have been developed to suppress the height
of a wire, leading to diversification of wire shapes.

[0007] Poor conduction or a defective shape that occurs after the wire
bonding in common wire bonding connection is handled as a failure in the
manufacturing process of ink jet heads. For a full-line type liquid
discharge head in which a plurality of recording element substrates is
arranged, however, many recording element substrates are mounted and the
number of wires to be connected increases, so that the probability that
poor connection in wire bonding occurs may increase. Thus, a
manufacturing yield of liquid discharge heads may be lowered, and
manufacturing costs may increase. Japanese Patent Application Laid-Open
No. 08-187860 discusses a configuration in which a plurality of wires is
stacked and connected to an electric connection portion connected by a
wire to reduce failures due to wire bonding. If the configuration is
used, even if an out-of-spec wire causing poor conduction is found by a
test after wire bonding, connection can be established by another wire
connected to the same connection portion, so that the manufacturing yield
of the liquid discharge head can be prevented from decreasing due to a
defective wire.

[0008] However, the following issue is found to occur if this
configuration is applied to an ink jet head. More specifically, according
to the configuration discussed in Japanese Patent Application Laid-Open
No. 08-187860, a plurality of wires with different heights is connected
to the same connection portion. Thus, the height of wires formed in the
end increases according to the number of wires connected to the same
connection portion and therefore, even if the low-loop formation
technique is used, the height of the wire located at the highest position
will be relatively high.

[0009] One effective element to improve print quality in an ink jet
recording apparatus is to make a head-to-paper distance smaller. The
head-to-paper distance is an interval between a discharge port surface on
which a discharge port for discharging ink droplets is formed and
recording paper that receives discharged ink droplets. If the
head-to-paper distance is large, deterioration in the print quality is
caused by lower precision with which ink dots are impacted onto the
recording paper or deformed dot shapes. One cause of the increasing
head-to-paper distance is the height of wires of wire bonding and the
sealing agent covering the wires. The height of the sealing agent is
almost the same as the height of wire and thus, making the wire height of
wire bonding as low as possible is effective in making the head-to-paper
distance smaller.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a liquid discharge head
including a wire bonding configuration that can decrease an occurrence of
defective head caused by defective wires in wire bonding and suppress an
increase in wire height.

[0011] According to an aspect of the present invention, a liquid discharge
head includes a recording element substrate including an energy
generation element for generating energy used to discharge a liquid and a
terminal electrically connected to the energy generation element, and an
electric wiring board including an electrode electrically connected to
the terminal via a wire to transmit an electric signal supplied from
outside to the energy generation element, wherein the terminal has an
area twice or more larger than a contact area between the terminal and
the wire and the electrode has an area twice or more larger than a
contact area between the electrode and the wire.

[0012] Further features and aspects of the present invention will become
apparent from the following detailed description of exemplary embodiments
with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate exemplary embodiments, features,
and aspects of the invention and, together with the description, serve to
explain the principles of the invention.

[0015] FIG. 2 is an enlarged view of a wire bonding portion of the liquid
discharge head in the exemplary embodiment.

[0016] FIGS. 3A and 3B illustrate a cross section of a wire connection
portion. FIG. 3A is a sectional view of a connection form in a first
exemplary embodiment, and FIG. 3B is a sectional view of the connection
form in a second exemplary embodiment.

[0017] FIG. 4 is a flow chart illustrating a wire bonding process.

DESCRIPTION OF THE EMBODIMENTS

[0018] Various exemplary embodiments, features, and aspects of the
invention will be described in detail below with reference to the
drawings.

[0019] FIG. 1 is a perspective view illustrating a liquid discharge head
H1000 having a wire bonding structure in a first exemplary embodiment and
an ink tank H1800 accommodating ink supplied to the liquid discharge head
H1000. FIG. 2 illustrates an enlarged view of a wire bonding portion of
the liquid discharge head illustrated in FIG. 1 and illustrates a state
before the wire bonding portion being sealed by a sealing agent.

[0020] A recording element substrate H1100 includes a board H1102 made of
silicon (Si) and a flow path member H1103 (see FIGS. 3A and 3B) formed on
the board H1102. The board H1102 includes an energy generation element
for generating energy used to discharge a liquid, a drive circuit
thereof, and a bonding pad H1101 which is an electrode terminal for
supplying a drive signal and electric power to the drive circuit. In the
present exemplary embodiment, the energy generation element is formed by
a heating element (heater).

[0021] A supply port for supplying ink corresponding to each energy
generation element is formed in the board H1102 constituting the
recording element substrate H1100. A discharge port H1104 through which
ink is discharged is formed in the flow path member H1103. A plurality of
the recording element substrates H1100 is arranged on a support substrate
H1200 made of alumina (Al2O3). A flexible electric wiring board
H1300 including a device hole H1302 which is an opening containing the
recording element substrate H1100 is arranged on the support substrate
H1200.

[0022] The bonding pad H1101 formed at an edge of the recording element
substrate H1100 and a lead H1303 which is a wire stretching from the
electric wiring board H1300 are electrically connected via a wire H1400.

[0023] A drive signal which is transmitted from outside the liquid
discharge head (a main body of the ink jet recording apparatus) to the
liquid discharge head and is an electric signal for driving the liquid
discharge head and power are input from a connector H1301 arranged on the
electric wiring board H1300. Then, the drive signal and power reach the
lead H1303 that is an electrode terminal of the electric wiring board
H1300 via a circuit wiring inside the electric wiring board H1300, then
are supplied to the recording element substrate H1100 via a wire.

[0024] In the wire bonding portion of the recording element substrate
H1100, a plurality of the bonding pads H1101 serving as electrode
terminals is arranged in one line along one side of the edge of the
recording element substrate H1100. The bonding pad H1101 has a
rectangular shape and is arranged in such a way that a short side thereof
is in a direction along one side of the edge of the recording element
substrate H1100 and long sides are mutually adjacent to each other.

[0025] On the other hand, a plurality of the leads H1303 serving as
electrode terminals is formed in the wire bonding portion of the electric
wiring board H1300. The leads H1303 face to the bonding pads H1101 of the
recording element substrates H1100 arranged inside the device holes H1302
and are arranged in one line along an opening side of the device holes
H1302. The lead H1303 has a rectangular shape and is arranged in such a
way that a short side thereof is in a direction along one side of the
opening of the device hole H1302 and long sides are mutually adjacent to
each other.

[0026] In the present exemplary embodiment, each of the bonding pads H1101
formed on the recording element substrate H1100 has a rectangular shape
and has bonding regions for wire bonding corresponding to the number of a
plurality of wires along a longitudinal direction thereof. The bonding
pad H1101 has a space, in which two or more regions each of which is
necessary for one (once) bonding can be arranged along the longitudinal
direction of the pad, in an exposure region where the pad is exposed. In
other words, the bonding pad H1101 has an area twice or more than a
contact area of the connection portion of a wire and the bonding pad.

[0027] For example, if the start-edge of ball bonding is bonded, it is
sufficient to provide a plurality of (two or more) regions larger than a
ground region of a crimping ball H1401 along the longitudinal direction.
The bonding pad H1101 in the present exemplary embodiment has, as
illustrated in FIG. 2, two regions (a first region and a third region)
each of which is larger than the ground region of the crimping ball H1401
and is formed along the longitudinal direction of the pad. More
specifically, the size of the bonding pad H1101 is set to 220*110 μm,
which allows two crimping balls H1401 for ball bonding whose crimping
diameter is about φ 90 μm to be grounded in the longitudinal
direction of the bonding pad.

[0028] Each of the leads H1303 of the electric wiring board H1300 has a
rectangular shape and has a plurality of bonding regions for bonding
wires along the longitudinal direction thereof. As illustrated in FIG. 2,
regions (a second region and a fourth region) in which two bonding
capillaries can be grounded are formed. More specifically, the size of
the lead H1303 is set to 230*120 μm, which allows two capillaries to
be grounded for bonding whose capillary ground diameter is about φ
100 μm.

[0029] FIGS. 3A and 3B illustrate a sectional view of a configuration in
which the bonding pad H1101 and the lead H1303 are connected by a wire,
which is a portion of the sectional view along the line FF' in FIG. 2. In
FIG. 3A, the start-edge of ball bonding in the bonding pad provided on
the recording element substrate H1100 is assumed to be the first region
on an edge side (electric wiring board side) of the recording element
substrate of the first region and the third region in which a region for
two bonding portions is secured. A ball bonding end-edge H1403 in the
lead H1303 provided on the electric wiring board H1300 is assumed to be
the second region, which is the opposite side of the recording element
substrate side from the center of the lead H1303 (electrode) in which a
region for two bonding portions is secured. Moreover, the wire H1400 is
assumed to have a shape in which main bending points are provided at
three locations.

[0030] The wire H1400 rises from the start-edge of ball bonding of the
bonding pad H1101 and is bent at a bending point 1 (H1410) at an angle of
90 degrees or more with respect to a direction perpendicular to the
surface of the recording element substrate, which is a wire connection
surface. In other words, after stretching in a direction (upward) away
from the support substrate H1200 from the start-edge, the wire stretches
toward the support substrate side (downward) via the bending point. Next,
the wire stretching from the bending point 1 (H1410) further stretches in
a direction (upward) away from the support substrate H1200 via a bending
point 2 (H1411). Then, the wire from the bending point 2 stretches toward
the support substrate H1200 side (downward) again via a bending point 3
(H1412). Lastly, the wire via the bending point 3 stretches to the ball
bonding end-edge H1403.

[0031] A case when, as illustrated in FIG. 3A, the bonding pad H1101 of
the recording element substrate H1100 is arranged at a position higher
than the lead H1303 of the electric wiring board H1300 will be described.
In such a case, it is necessary to secure a large edge clearance E to
prevent the wire from coming into contact with the recording element
substrate while suppressing the maximum height of the wire. For this
purpose, the wire shape is adjusted in such a way that the bending point
1 (H1410) becomes the highest point of the wire. Compared with a wire
shape having one bending point, three bending points as illustrated in
FIG. 3A can be employed because if the wire is deformed, each bending
point is displaced or deformed, so that an increase in the maximum height
of the wire can be suppressed and the head-to-paper distance can be
secured. In other words, many bending points can be employed because when
a wire is deformed, a deformed amount can be absorbed by each bending
portion and regions between the bending portions.

[0032] If the first region or the second region of each electrode terminal
in the above configuration is selected, the third region and the fourth
region that can be used for wire bonding remain in each electrode
terminal region after electrodes are connected by wire bonding. In the
present exemplary embodiment, the start-edge of wire bonding is provided
on the recording element substrate H1100 edge side (first region) of the
connection region which is provided more than one in the bonding pad
H1101. Such configuration is preferable because the large edge clearance
E, which is the distance between the wire and board surface, can be
secured at a board edge where the wire H1400 for connecting between
electrodes easily comes into contact with the recording element substrate
H1100.

[0033] It is assumed in the present exemplary embodiment that there are
two regions which can be used for wire bonding, however, it is only
necessary to secure two or more regions. Regarding the distance between
connection regions, the interval between the first region and the second
region and the interval between the third region and the fourth region
may be different. Further, combinations of connection regions are not
limited to the connection between the first region and the second region
and the connection between the third region and the fourth region. The
connection between the first region and the fourth region and the
connection between the second region and the third region may be used as
long as both of the maximum height of the wire and the edge clearance
fall within desired ranges. Furthermore, the wire bonding method between
the electrode terminals is not limited to the ball bonding, and wedge
bonding may also be used.

[0034] In a second exemplary embodiment, a configuration is described
which, when an out-of-spec wire causing poor conduction is found by a
test after wire bonding and poor electric connection occurs between the
electrodes, electrically connects between the both electrodes by
re-forming a wire in the regions which remain in both electrodes and can
be used for wire bonding. In the present exemplary embodiment, an
electrical characteristic test of the liquid discharge head is performed
to check for any occurrence of defect in the wire-bonding portion after
the wire-bonding process described in the first exemplary embodiment
ends. FIG. 4 illustrates a flow chart of a wire bonding manufacturing
process.

[0035] First, as described in the first exemplary embodiment, the first
region and the second region of each electrode are connected by wire
bonding (first connection step: 402). Next, in step 403, an electrical
characteristic test of the wire is performed.

[0036] If a test result is OK (OK in step 403), the process proceeds to
the next process (step 409). If the test result is determined to be no
good (NG in step 403), then in step 404, whether the cause thereof is a
specific wire failure is determined. If, as a result of the analysis, the
cause is a specific wire failure (YES in step 404), wire bonding is
performed again. If another failure is the cause (NO in step 404), then
in step 406, measures are taken separately if necessary.

[0037] The configuration when wire bonding is performed again is
illustrated in FIG. 3B and the flow thereof is illustrated in FIG. 4.
When wire bonding is performed again, the third region and the fourth
region that are free regions remaining in the electrode terminals are
used. However, before performing the wire bonding to the third region and
the fourth region, it is necessary to remove the specific defective wire
formed between the first region and the second region (step 405).

[0038] As a method for removing a wire, pulling out by a wire clamp
operation and a peel strength test operation performed by a tweezers peel
strength test apparatus or pulling out by a micro-manipulator can be
applied. If a distance between adjacent wires is relatively large, the
wire can be pulled out by manual work using tweezers. In all cases, it is
necessary to remove the defective wire in such a way that adjacent normal
wires are not deformed or damaged.

[0039] After the defective wire is pulled out, it is necessary to prevent
a portion of the crimping ball H1401 remaining in the first region of the
bonding pad H1101 from exerting an influence such as coming into contact
with a capillary when wire bonding is again performed to the third region
adjacent to the first region. Thus, the crimping ball H1401 needs to be
completely removed from the bonding pad H1101 without any residue or to
be thinly processed (as portion H1402) to such an extent that no
interference occurs with the re-formed wire H1400.

[0040] Processing methods may include peeling from the board by tweezers
of a bump pull test, peeling or shearing using shear tools of a shear
strength measuring apparatus, and a squash method by a flip chip bonder.
Also in this case, a method that does not deform or damage adjacent
normal wires may be used (step 405 in FIG. 4).

[0041] In the liquid discharge head in which wire bonding is performed
again (second connection step: 407) for a portion of wires as described
above, a plurality of types of wire bonding is mixed. In other words, a
wire (first wire) connecting the first region of the bonding pad H1101
and the second region of the lead H1303 and a wire (second wire)
connecting the third region of the bonding pad H1101 and the fourth
region of the lead H1303 are mixed.

[0042] FIG. 3B illustrates the configuration in which the third region of
the bonding pad H1101 and the fourth region of the lead H1303 are
connected by a wire. The start-edge of ball bonding to the bonding pad
H1101 is the third region and the ball bonding end-edge H1403 to the lead
H1303 is the fourth region. In this case, the wire H1400 has a shape
different from the configuration in FIG. 3A illustrated above and
includes bending points provided at two locations. The wire rises up from
the start-edge of ball bonding of the bonding pad H1101 and has a bending
point 4 (H1413), at which the wire is bent at an angle of 90 degrees or
more with respect to a direction perpendicular to the surface of the
recording element substrate, which is the wire connection surface. In
other words, after stretching in a direction (upward) away from the
support substrate H1200 from the start-edge of ball bonding, the wire
stretches toward the support substrate side (downward) via the bending
point 4 (H1413).

[0043] Next, the wire stretches toward the support substrate H1200
(downward) again via a bending point 5 (H1414) following the bending
point 4 (H1413) and further stretches toward the ball bonding end-edge
H1403. If the bonding pad H1101 of the recording element substrate H1100
is arranged at a position higher than the lead H1303 of the electric
wiring board H1300, the configuration described below can be employed.
More specifically, in order to secure a large edge clearance E' while
suppressing the maximum height of the wire, the wire from the bending
point 4 to the bending point 5 may stretch in a direction along the
surface of the recording element substrate, preferably substantially
parallel to the surface.

[0044] Such a wire shape can be employed since the large edge clearance E'
can be secured even when the third region whose board edge is apart from
the bonding region used for connection in the recording element
substrate. Further, by employing such a configuration, the ball residue
remained in the first region after removing the defective wire can be
prevented from coming into contact with a wire.

[0045] Accordingly, even when wire bonding is performed again, the maximum
height of the wire can be made comparable to the maximum height of the
wire of normal wire bonding. In other words, if the recording element
substrate is higher than the electric wiring board, it is preferable that
the first region and the second region can be connected by the wire for
the initial electric connection, and the third region and the fourth
region are connected by the wire when electric connection is established
again after a failure.

[0046] The length of the wire (second wire) used to connect the third
region and the fourth region is substantially equal to the length of the
wire (first wire) used to connect the first region and the second region,
so that the length of the wire formed between each region can be
substantially equal. Accordingly, wire expansion and contraction due to a
temperature change becomes substantially the same among the wires, and
thus, a difference of connection reliability of wire bonding can also be
suppressed.

[0047] In step 408, after the wire bonding is performed again, an electric
test of the wire bonding portion is performed. If no failure is found,
then in step 409, the process proceeds to the next process.

[0048] In the present exemplary embodiment described above, the first
region and the second region are first connected by wire bonding and the
third region and the fourth region are connected for a defective portion.
The present invention is not limited to the above example and may employ
a connection in a reverse manner. However, if an influence of an edge
touch is taken into consideration, it is preferable to connect the
relatively higher side from the support substrate H1200, that is, the
first region closer to an edge of the recording element substrate H1100
first. Accordingly, an occurrence of failure due to the edge touch can be
reduced when compared with a case of using the third region.

[0049] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all modifications, equivalent structures, and functions.

[0050] This application claims priority from Japanese Patent Application
No. 2010-137472 filed Jun. 16, 2010, which is hereby incorporated by
reference herein in its entirety.